Large scale computer systems incorporate banks of mass storage units such as arrays of hard disk drives. Hard disk drive units currently available for this application typically employ 3.5 inch drives configured into one of two "height" form factors: one inch and 1.6 inch. Each disk drive is about four inches in "width". The height and width dimensions are stated for industry categorization purposes only because the disk drives will operate in any orientation and are often arranged with the "height" dimension disposed horizontally; for example, in conventional nineteen inch rack mounts.
At the state of the art, the performance characteristics of 1.0 inch and 1.6 inch form factor disk drives may be summarized as follows:
The 1.6 inch disk drives generally have higher capacity and offer lower cost per unit of storage provided (i.e., cost per megabyte).
On the other hand, the one inch disk drives generally are less costly per disk drive and offer higher performance.
Disk drives in servers or disk subsystems are usually packaged in canisters which permit L ion of the disk drives including the support of hot plug/unplug functions. The canisters each have a connector adapted to engage a complementarily configured connector on a backplane which includes printed circuit traces conventionally interfacing with system circuitry. The position and orientation of a canister connector is typically established by an industry standard for the type of mass memory unit employed. Thus, because the mechanical dimensions of the disk drive caters and the electrical and mechanical interfaces are well defined into a respected standard, a ready interchange of canisters may be carried out.
It is common practice to include disk drive canisters in each of the one inch and 1.6 inch form fax in a given system to achieve an optimization of performance and storage capacity for the application. In the prior art, this has been achieved by adopting an electrical and mechanical design which directly supports the 1.6 inch disk drive canisters and which also accommodates the one inch disk drive in the same canisters. With this approach, however, the one inch disk drive canisters occupy the same "height" dimension as the 1.6 inch disk drive canisters. This approach is very easy to put into practice, but completely fails to allow the achievement of optimum space usage, and this is a significant drawback.
Of course, two different designs accommodating, respectively, a row (for example, in a standard nineteen inch rack mount) of one inch canisters and a row of 1.6 inch canisters can be provided, but this approach does not permit optimally mixing one inch and 1.6 inch canisters in a given row, and the advantage of the use of a single backplane and mechanical design is lost.